dhclient Nor Starting (KVM, CentOS)

I have some 12 VMs under a KVM environment on CentOS 6.4. Initially, they all had the NetworkManager service enabled, until it was evident that it was interfering on the server itself with the bridged networking configurations, which it doesn't support. (It killed dhclient).

After much searching I found that in a server environment it is not a best practice to have NetworkManager enabled. So I disabled it not only there but on all my servers.

So far, the machines have worked fine (> 1 month) - only that today I rebooted one of them and to my surprise, dhclient didn't start despite being correctly listed in the /etc/sysconfig/network-scripts.
Now I've tried with a 2nd one, same results. dhclient is not starting.

dmesg shows that eth0 was being renamed to eth1 and know that if this conflicts with the contents of /etc/udev/rules.d/70-persistent-net.rules this will cause trouble, but even updating there gets no fix on the dhclient start...

Wouldn't dhclient just start when the ifup gets executed (and remain as a daemon), not needing to be listed under init.d?

Thanks for your response. Although the marked parameters in ifcfg-eth0 were there, a 2nd check on this file found that for some reason the MAC was wrong. Putting the correct MAC fixed the issue - now the server asks for IP at boot, as needed.

Remarkably, that "bad" MAC address was also listed under the /etc/udev/rules.d/70-persistent-net.rules mentioned in the post - A few months ago I had run into similar trouble there when swapping disks on identical servers, as it carried over the MAC data from the original server. But this was not the case here, as this was a new VM. The suggested solution in such case was to delete the file (it regenerates itself). That's the reason I was digging also there.